Creep and rupture of an advanced fiber strengthened eutectic composite superalloy
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Chill cast ingots of NiTaC-13 of composition in wt pct: 3.3 Co, 4.4 Cr, 5.4 A1, 8.1 Ta, 0.54 C, 3.1 W, 6.2 Re, 5.6 V, balance Ni, were directionally solidified in a Bridgman furnace at a rate of 6.35 mm/h in a
D. A. WOODFORDis Staff Metallurgist, Corporate Researchand Development, GeneralElectric Company, Schenectady, NY 12301. Manuscript submittedSeptember 13, 1976.
Fig. 1--Transverse section showing TaC fibers in a 7-7' matrix.
METALLURGICAL TRANSACTIONS A
perature. Treatment of the two b a s i c problems in these a r e a s , namely, the development of a constitutive c r e e p equation to provide input t o time dependent analysis of nonsteady test conditions, and the e x t r a polation of short time rupture data to predict s e r v i c e lives, is covered. Thus, t h e r e is no attempt to interpret the data in t e r m s of specific deformation mechan i s m s or history independent rate equations which have been singularly unhelpful in the p a s t . However, the special microstructural features, of this and s i m i l a r alloys, may have a profound effect on the high temperature behavior and this will be discussed. EXPERIMENTAL
PROCEDURE
VOLUME 8A, APRIL 1977 639
7 t
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measurements. S i m i l a r e x t e n s o m e t r y was used f o r the air c r e e p t e s t s . Rupture t e s t s o n the smatter specimens were p e r f o r m e d without s t r a i n m e a s u r e ment.
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zlf I ~ i_ 0
200
RESULTS i) A n a l y s i s of C r e e p D a t a
400
600
800
I000
~200
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I 1600
1400
1800
T I ME, H R
Fig. 2 - - C r e e p c u r v e s at 871°C in a r g o n . D a s h e d c u r v e s a r e computed. 7
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1093"C
ARGON
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Cro(1
103MP,', 5 117.2
~ 4 3¢..,
+ e) : C(t) H(e)
[1]
w h e r e Cro i s t h e i n i t i a l s t r e s s , E i s t h e e n g i n e e r i n g s t r a i n a n d C(t) a n d H(e) a r e f u n c t i o n s of t i m e a n d s t r a i n . T h i s relationship between true s t r e s s (ass u m i n g constant volume and uniform deformation) a n d the p r o d u c t o f f u n c t i o n s of t i m e a n d s t r a i n m a k e s no p r i o r c o m m i t m e n t t o t h e f o r m of t h e e q u a t i o n a n d yet incorporates as s p e c i a l c a s e s m a n y o f t h e m o r e p o p u l a r c r e e p e q u a t i o n s s u c h a s t h e p o w e r l a w of B a i l e y6 i n w h i c h
6
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F i g s . 2 a n d 3 s h o w s e t s of c r e e p c u r v e s i n a r g o n a t t e m p e r a t u r e s of 871 a n d 1 0 9 3 ° C . T h e c r e e p c u r v e s show an initial transient s t r a i n with a m i n i m u m occ u r r i n g a t a b o u t 1 p c t c r e e p . T h e r e w e r e no c l e a r irregularities in c r e e p to i n d i c a t e f i b e r f a i l u r e a n d in g e n e r a l n o u n u s u a l b e h a v i o r e x c e p t f o r t h e s h a r p i n c r e a s e i n c r e e p r a t e a t t h e e n d of the t e s t i n t h e l o w e r s t r e s s t e s t s at 1093°C. T o develop an isothermal c r e e p equation, a recently developed m e t h o d which has b
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